1. Field of the Invention
This invention relates generally to oil well cementing compositions and specifically to polymeric fluid loss additives for such compositions and methods of making the same for controlling fluid loss during cementing operations.
2. Cross Reference to Related Applications
This application is related to the copending application, Ser. No. 683,787; entitled "NON-RETARDING FLUID LOSS ADDITIVES FOR WELL CEMENTING COMPOSITIONS", by Lee Frederick McKenzie, Paul Michael and Dyke William Reese, filed concurrently herewith.
3. Description of the Prior Art
Cement compositions are used in the oil and gas industry to cement the annular space in the well bore between the surrounding formation and pipe or casing. Typically, the cement slurry is pumped down the inside of the casing and back up the outside of the casing through the annular space. The amount of water which is used in forming the cement slurry will vary depending upon the type of hydraulic cement selected and the job conditions at hand. The amount of water used can vary over a wide range, depending upon such factors as the required consistency of the slurry and upon the strength requirement for the particular job. Many times, the hydraulic cement must be placed within or next to a porous medium, for example, earthern strata in the well bore. When this happens, water tends to filter out of the slurry and into the strata during the settling of the cement. Many difficulties are related to an uncontrolled fluid loss of this type such as an uncontrolled setting rate, improper placement of the slurry, imparied strength properties, and contamination of the surrounding strata. These conditions are all undesirable in oil and gas well cementing operations.
In order to lessen the loss of fluid from the aqueous cement slurry, various materials have been employed in the past. One such material was a copolymer of an acrylamide and acrylic acid. This fluid loss material had the ability to maintain fluid loss control over a wide temperature range, functioned well in the presence of salts, and was superior to cellulouse base additives when chloride salt accelerators were present. In spite of these advantages, the copolymer of acrylamide and acrylic acid exhibited latent retarding effects, thereby lessening the usefulness of such material at lower temperatures.
In a study of the retarding effects associated with the acrylamide/acrylic acid copolymer, it was theorized that the source of the retarding effect was the generation of carboxyl groups by gradual hydrolysis of the amide functionality. The present invention is the discovery that the latent retarding effects of the acrylamide/acrylic acid type copolymers can be eliminated by substituting for the acrylamide certain cationic and non-ionic monomers.